I am using LM2596 for a dc supply where I could alter the output voltage. Datasheet here.
I have setup according to page 9 "Adjustable Output Voltage Versions". Everything worked fine. The output voltage alters as I changes the value of R2 (potentiometer used for R2, R1 remains 1K).
Now, I was thinking that the feedback pin is just taking a the voltage potential between R1 and R2. Thus instead of using R1 and R2, I supply a voltage (0-2V) from the bench power supply directly to the feedback pin. But as I vary the bench power supply, the output voltage does not vary. The power supply and the chip is common grounded.
Why is that? When using R1 and R2, the voltage on the feedback pin is around 1.3V. Removing R1 and R2, and supply feedback pin with a 1.3V does not yield the same output voltage. Or must there be a certain current flow?
The final destination would be to digitally control the chip (e.g. using a digital potentiometer or DAC).